1. Field of the Invention
The present invention relates to a motor drive camera, which carries out the film winding up, the film rewinding and the exposure operation by means of a motor drive device.
2. Description of the Prior Art
Quite recently, the camera with a built-in motor drive device has been brought to practice. What is most important is the balance between the efficiency of the winding up device and that of the camera. In order to raise the efficiency of the winding up device, it is necessary to increase the number of batteries to be built in the camera, while in order to increase the operativity of the camera it is necessary to make the camera compact. These demands are contradictory. In order to overcome this contradiction it has been proposed to mount the auxiliary power source if such a manner that in the operativity is the first consideration the winding up device is driven only by means of the power source built in the camera body. If the film winding up speed is the first consideration, the winding up device is also driven with the auxiliary power source mounted on the camera body. However, if the winding up speed of the winding motor is increased with the auxiliary power source, the following problems develop.
The time setting of the safety timer is the problem. Until now in order to avoid perforation damage at the end of the film in a camera with the built-in motor winding up device, a safety timer operatively engaged with the start of the motor is provided in the motor winding up device in such a manner that if a winding up finish signal is not produced, even after a certain predetermined winding up time has elapsed, the motor is stopped, on the assumption that the film has been finished or the power source voltage has been abnormally decreased.
Consequently, if by adopting the auxiliary power source the winding up time becomes shorter than in the case of power being supplied only from the camera body, the safety timer time set, in accordance with the winding up time, in the case of only the camera body is so long that there is a possibility that the film perforations may be damaged by the tension itself imposed on the film due to the earlier completion of the film winding up during the set time or due to some other causes during the film winding up. It is necessary for the photographer who uses such a camera to always take care of the number of remaining picture frames of the film, which is inconvenient.
In such a camera the rewinding speed of the film is also another problem.
Secondly, in case the film is rewound at a speed higher than a certain determined one, the static electricity takes place between the film and the press plate or between the film and the partone in such a manner that there is a damage that the film is exposed with a spark due to static electricity. Consequently, in the above-mentioned camera, where the auxiliary power source is utilized the voltage applied to the motor is higher so that when the film is rewound the rewinding speed is unnecessarily high, which causes inconvenience.
On the other hand, it is not necessary for the rewinding speed to be as high as with the winding up speed.